1. Field of the Invention
This invention relates generally to a method of revocation and updating of tokens in a public key infrastructure (PKI) and, more particularly, to a method and computer program for managing encryption, signature and role certificates/private keys contained in a token.
2. Discussion of the Related Art
For centuries individuals, governments, and business entities have searched for mechanisms and techniques whereby sensitive information may be transmitted to authorized parties over long distances and still remain secure. The problem faced by the foregoing entities is how can information be sent to the individual or entities that require it and still be assured that unauthorized parties may not be able to comprehend the transmitted information should they intercept it. Early methods of securing information have employed scrambling techniques, lookup tables, substitution ciphers, and code books in which letters or terms would be substituted for the original letters and terms in the information. These techniques frequently required that both the sender and receiver of information have access to the same “code book”. One danger in such a technique is that the code book would fall into unauthorized hands.
In the early twentieth century, and in particular during World War II, code books were replaced by electromechanical cipher machines. Both the sender and receiver would have an identical cipher machine used to encrypt and decrypt messages sent. In order to make it more difficult to decrypt these messages the cipher machines have the ability to change the cipher used in a message or change the cipher used for every few words within a message. In order to accomplish this the cipher machine would need to know the initial state or key utilized to encrypt the message.
In recent years cipher machines have been replaced by digital encryption algorithms in which both the sender and receiver have an identical copy of the digital encryption algorithm and a common key used to encrypt and decrypt messages. Both the encryption algorithm and key are held secret by both the sender and receiver.
More recently another encryption technique has been developed in which two separate keys are used for encryption and decryption. A public key is transmitted freely to whoever requires it and is used to encrypt messages for a particular receiver. The receiver would have an associated private key which may be used to decrypt the message encrypted with the associated public key. For each public key there is only one private key and for each private key there is only one public key. When sending a message to several recipients it is necessary to have each recipient's public key. The message would then be separately encrypted using each recipient's public key and transmitted to that particular recipient. Therefore, if ten separate entities are to receive the same message, ten separate messages would be transmitted with each message encrypted with individual's public key. With the advent of the Internet, such a public key infrastructure has gained significant acceptance as discussed in request for comments number 2459, by Housley et al., entitled “Internet X.509 Public Key Infrastructure”, herein incorporated in its entirety by reference.
In addition to the need for the encryption and decryption of messages, with the advent of electronic mail and the Internet a need has developed for a secure mechanism to indicate approval and acceptance by an individual. In the past an individual would typically show his approval or acceptance of such items as a contract or an order via a handwritten signature, a stamp, or a seal which would only be held by that individual. Anyone else that attempted to imitate such a signature, stamp, or seal would be subject to criminal penalties. With the advent of electronic mail and the Internet, a need has arisen to take advantage of the ease and speed of electronic mail to indicate, by a person or entity with proper authority, approval or acceptance of a contract or purchase. This has come to be known as a digital signature in which an individual may digitally sign a document.
This digital signature capability has been implemented using the same public key infrastructure previously discussed. However, instead of an entire document being encrypted, the document itself is passed through a one-way hashing algorithm that produces a small document, referred to as a digest. This digest is then encrypted using the individual's private key, also known as a private signing key, and is appended to the document. The receiver of the document can verify the authenticity of the digital signature (digest) by stripping the signature from the document and recomputing the hash function on the document to generate an as received digest. Using public signing key, included in the document or previously received, it is possible to decrypt the digest of the document and compare it to the digest as recomputed. If the two digests match, then the signature is authenticated and the document received is proved to be identical to the document signed by the sender. Therefore, using the aforementioned public key infrastructure it is possible to both encrypt and decrypt messages as well as digitally sign documents.
However, in the aforementioned public key infrastructure, several limitations exist. One such limitation is in order for a group of individuals or entities to transmit and receive the encrypted messages each individual must have created a key pair having a public key and a private key. Further, each individual or entity in a group is also required to have a separate public signing key and a private signing key in order to digitally sign documents. In order for other members of the group to be able to decrypt messages received it is necessary for members of the group to exchange key pairs including the private key. This may be necessary when a member of the group is not in the office due to illness or travel. Where such an exchange of key pairs does not take place, when an urgent encrypted message comes into, for example, the office of finance, human resources, or an engineering group in the corporation, only the person holding the private key may decrypt the message. When that person is unavailable, that message will not be decrypted and a prompt response will not be received by the sender. However, when key pairs are exchanged by members of a group, then all members who possess an individuals private key may decrypt all messages sent to that person, regardless of the nature the message or its sensitivity. This creates significant problems for businesses that need to respond quickly to customer requests and in which customer confidences must be maintained. This may most acutely be seen in law offices, medical offices and the military where delay in delivering a response may be very costly. Further, it is cumbersome for a large group of individuals or entities to exchange key pairs with one another. For example, where group contains 30 individuals, a total of 30 times 30, or 900 exchanges of key pairs must take place in order for anyone in the group to be able to decrypt any message received by any other member of the group.
Another limitation that exists deals with security and portability of certificates/private keys. Typically, certificates assigned to users have both private and public keys with each stored on a computer. These certificates/private keys are often limited to usage in those computer systems in which they are stored. Therefore, if a user desires to use another computer system he must move his certificates/private keys to that system. Further, personal computers connection to the Internet have proven to be vulnerable to infiltration and damage by unauthorized parties. Therefore, if private keys for encryption and signature certificates/private are stored on a personal computer which is directly or indirectly connected to the Internet, it is possible to copy the certificates/private keys and with some effort to determine the passphrase required to use the certificates/private keys.
Still another limitation to these certificates/private keys is that they are limited to usage in and between computer systems for exchange of digital information or signature purposes. It is often necessary in a corporation or government entity for certain physical areas to have restricted access. Normally, these areas are protected by security guards who check badges to allow access by individuals. However, these badges may not necessarily be authentic or current. Therefore, an individual whose access to a particular area has been revoked may still enter that area if he retains his badge.
Therefore, what is needed is a method and computer program in which certificates/private keys may be stored on a portable device that may be easily physically carried by an authorized user. This physical device should be able to contain a significant number of certificates/private keys assigned to that user. Further, this physical device should be readable by a computer system that is not necessarily the normal computer system accessed by the user. The certificates/private keys contained within this physical device should be able to operate in the same manner as any other encryption or signature certificates/private keys in a PKI system. In addition, these certificates/private keys should be protected from unauthorized access in the case of loss or theft. Still further, this physical device should also contain a special class of certificates/private keys which represent a role or organizational group and would allow an authorized user access to information for that group and the ability to make commitments or indicate approval on behalf of the group. Still further, this physical device should be of such a nature to be used as an identification means for access to restrictive areas and information.